Circumventing and avoiding a neutralizing or toxic immune response against a gene therapy vector is a major challenge with all gene transfer vector types. Gene transfer to date is most efficiently achieved using vectors based on viruses circulating in humans and animals, e.g., adenovirus and adeno-associated virus (AAV). However, if subjects have been naturally infected with a virus, a subsequent treatment with a vector based on that virus leads to increased safety risks and decreased efficiency of gene transfer due to cellular and humoral immune responses. Capsid antigens are primarily responsible for the innate and/or adaptive immunity toward virus particles, however, viral gene-encoded polypeptides also can be immunogenic.